Twenty years ago I owned a turbo charged '87 Toyota Supra. At about 75k the head gasket failed. The service guy at the dealer said well it’s an aluminum head on a cast iron block - (inline 6) it’s a wonder you got as far as you did. I learned at that point, from conversations with other Supra owners, that there were two types of Supra’s, those with a new head gasket and those that needed … you get the drift. A miserable and unreliable car in so many ways.
Forty five years of multiple XK engine ownership, hundreds of thousands of miles, racing and autocross, and years of involvement with JCNA and it’s members, I’m trying to recall if I’ve ever even heard of a head gasket failure. I’m sure there have been some somewhere, but it’s gotta be really rare, and I suspect caused mostly by bad rebuilder practices.
Robert
Yes…true…but I suspect the underlying reason for the longer studs is a further benefit of the length change and tension relationship,you have mentioned. This is a classic solution to eliminate fatigue failure. The bolts are thin flexible rods compressing a more stiff lump of steel or aluminium. Any movement of the cylinder head as a result of internal pressure results in a sharing of this load between the block and the studs. Because of the flexibility difference the studs only experience a small increase in load and…in essence…the life of a fastener is heavily dependant on the magnitude of the fluctuating load…(and also the mean stress in the bolt). Less magnitude …longer life …this is textbook Mechanical Engineering…and I suspect that the Jaguar Engineers involved in the engine design would,have known this theory…
Regards
Matt
I was plumbing the archives on the subject and came upon this thread. An educational and entertaining read on a quiet Sunday night with a glass of very nice Malbec.
Hmmm. I’m being quizzed about resurrecting a zombie thread
but I’ll ask my questions anyway. Forgive me if I’ve stirred up some dust on well ploughed ground ….
I recently had a challenge removing a few of the 14 studs from my short stud E-type head after lifting it. When I did the engine refresh 10 years ago I reused the original studs and didn’t know enough to reinstall them with a thread sealant. They backed out of the block with some effort but got stuck in the head. Oil had crept up into the bolt passages in the head and cemented those few studs in place with a black crud. It took heat and penetrant and slide hammering to get them out. New studs en route.
As I understand it, thread sealant will prevent a repeat.issue in this short stud engine, the same in a long stud engine so long as the coolant is changed regularly, but do the long studs sometimes rust away in their bolt passages in the head and also lock them in place?
Does the long stud engine have more mass and rigidity with the casting extending through the oil gallery into the water jacket?
I’m on a roll.
Stainless steel studs a solution for the long stud engine?
Why does the long stud engine feature double the frost plugs of the short stud engine?
In my experience, yes, yes they do. One thing to remember about corrosion - rust is when steel rusts the volume of the material expands. That’s one of the reasons concrete can crack, the rusting rebar expands and cracks it. There may also be a reaction between the corroding steel and aluminum that causes the head to want want to stick to the studs.
Almost always, unless the engine has been absolutely perfectly maintained all its life
The stud will often rust through near the base and snap off flush
The steel studs can corrode the female threads un the iron block
All very bad things which are expensive to repair
I agree some sort of thread sealant should be used
What kind is the question
In the case of long stud motors, there is also a tendency for the studs to wind out when the head nut is turned, which is very bad if any coolant is present, as it will fill the hole
For a long stud motor, I have experimented with red oxide 2 pack primer on the unthreaded stud, Loctite Screw Lock for the base of studs (watertight, only has a light locking action), copper slip for the stud cap nut
As for SS, their maybe some problems @Mike_S may be able to comment on that
On short and long stud heads, I always put a fillet of RTV right at the exit of the stud/block, before installing the head. That kept oil and coolant down and the couple of times that I re-pulled a few heads that I had done that on, there was much less gunk between the head and the stud.
Both the long and short studs can make head removal difficult - don’t know if there is much difference, as coolent gets up inside of both. They both rust. The one below is a short stud I removed from an engine 30 plus years ago.
I raced an E Type for 15 years and did my own engine work (not the machining). It was generally accepted as a truth among the racers that the long stud engine, where the studs goes into each bearing casting, was a better engine to use as a race engine, but the later XJ6 blocks had other things going for them as well, which were arguably more important. Some say that the studs that go only into the deck distort the deck somewhat when tightened as opposed to the long studs where any bore distortion can be dealt with by using a torque plate.
Stainless steel studs - the purpose of torquing down the head to a specific torque is to cause the studs to stretch slightly into their elastic range. This prevents the nuts, which use no other locking method, unwinding as the engine is used. I’ve got no idea if s.s. offers the same benifit - do they stretch and remain elastic, and at what torque? There are some pretty exotic studs out there of special composition eg air cooled Porsche, so maybe something is available?
I have never personally seen a 2.4, 3.4, 3.8 or short stud 4.2 block where the heads studs have pulled up the deck, but I have many, many, long stud 4.2’s with sheared off studs, which in the 80’s and 90’s generally led to the car being scrapped as the cost of repair far exceeded the car’s value.
I don’t believe the short studs extend into the water jacket, so there should be no coolant getting up into the head to cause corrosion, more likely to be electrolytic reaction between the steel and aluminium.
I must admit I’ve never understood why coolant never came up the studs and out under the D washers in the long stud engine even in a good engine considering it isn’t really sealed with anything other than torque and hopefully clean flat surfaces.
Just for the record, the long stud engines are the latest iterations, introduced around the time of S2 E Type, 420G and XJ6, ( 1968ish). Bore distortion can be dealt with on either type of block.
That was exactly what led me to painting some with 2 pac red epoxy bare metal primer, its very non-porous as it dries by chemical reaction, so there is many factors less of solvent evaporation
Some of those studs are in a long stud 4.2 motor that I will probably have to strip down (its the original matching numbers motor from my 420G, used too much oil, got swapped out)
These are the studs I’ve just extracted, after bead blasting. Two lengths, 6 1/2” and 6 3/4”. Some of the shorter studs are pristine, a few show some light corrosion. The four longer studs, including the dowel stud, are noticeably more pitted and it was three of these four that seized in the head with black crud.
Nick - are you doing a total engine overhaul?
If so, I was sent 6x pairs of 6-cylinder rod bolts (years ago) when I ordered rod bolts for my V12.
If interested, PM me. cheap
